Wasn't Mr. Gray one of the aliases that arcade scam group used to book appointments? 👀 I can't remember their name. You know what I mean; the ones who "upgraded" units in like two hundred different arcades with trick coin collectors lol. I know there's not a lot of evidence of them after the early 90s, but still... maybe OP misremembered the timing & they were experimenting with just manufacturing whole machines? Harder to get caught if you're just delivering a cabinet rather than spending a couple hours tinkering...
ETA: I might be mixing them up with Grey Horizon who did the weighted ball grift. Can you tell I've been mainlining the Bumper Bumbles podcast on my commute lol